Recently, as industries such as a data center and artificial intelligence (AI) advance rapidly, it is required to transmit or receive more data for a short time, and thus, optical communication technology is attracting much attention. Therefore, miniaturizing and speeding up of an optical transceiver module which performs a core function in optical communication are needed.
An optical transceiver module for optical communication includes an optical sub assembly (OSA) unit for performing conversion (optical-to-electric conversion/electric-to-optical conversion) between an optical signal and an electrical signal and an electrical sub assembly (ESA) unit for performing signal processing on an electrical signal.
Here, the OSA unit includes a transmitter optical sub assembly (TOSA) which converts an electrical signal into an optical signal and transmits the optical signal and a receiver optical sub assembly (ROSA) which converts a received optical signal into an electrical signal.
In order to secure maximum optical coupling efficiency in manufacturing core elements such as the TOSA and the ROSA, precise optical alignment of optical devices such as a laser diode (LD), a photodiode (PD), a mirror, a lens, and a waveguide in an optical transceiver is needed.
In a single mode optical fiber, a diameter of an optical waveguide core is about 9 μm, and in order to secure maximum optical coupling efficiency, an optical alignment error of a lens is allowed within a range of several μm or less.
In recent trend, as miniaturizing and speeding up of optical modules are needed, the use of multichannel optical modules is increasing rapidly. Also, in order to decrease a size of each of the optical modules, a refractive index difference between a core and a cladding of a waveguide included in the TOSA/ROSA increases, and thus, a thickness of a core layer is reduced by about 3 μm.
Therefore, sensitivity to optical alignment has more increased, and due to this, cost and time are expended in an optical aligning and bonding process for a lens in packaging optical elements.
Generally, as illustrated in FIG. 1, the lens is inserted into a space between the waveguide and the LD for optical alignment of the LD and the waveguide, and then, the amount of light incident on the waveguide is maximized by adjusting a position to three X-Y-Z axes.
In this case, after the position is optimally adjusted by finely controlling the lens, epoxy is injected into a space between a lower end of the lens and an optical module platform substrate, and then, by hardening the epoxy with light having a thermal or ultraviolet (UV) wavelength range, the lens is fixed.
A process of hardening the epoxy used to fix the lens has a feature where the epoxy is changed from an initial liquid state to a gel state corresponding to a semisolid state by using heat or light having the UV wavelength range, and then, is hardened to a solid state.
At this time, a hardener included in the epoxy evaporates while the liquid state is being changed to the solid state, and thus, a contraction process where volume of the epoxy is reduced is accompanied.
In relate art, in a lens assembly process using epoxy, a contracting force based on epoxy contraction is generated between a lens and a platform substrate, and the contracting force acts as a force for changing a position of the lens.
In a general lens assembly process, a holder such as a lens gripper strongly grips a lens, for maintaining a position of the lens as an initial maximum optical alignment point against the contracting force.
However, as illustrated in FIG. 2, after an epoxy hardening process ends, the position of the lens is maintained by force balance between an epoxy contracting force and a gripping force based on the lens gripper. Finally, when the lens is separated from the lens gripper, a lens gripping force is removed, and due to this, force balance is disrupted, whereby a position of the lens is moved in an epoxy contracting direction from an initial alignment position by a force acting in the epoxy contracting direction. For this reason, optical coupling loss occurs due to changing the position of the lens.
In order to solve such a problem, recently, a hardening time increases by reducing energy of UV for hardening epoxy or reducing a hardening temperature, and thus, a time of a process of changing a gel state to a solid state increases in the epoxy hardening process. The gel state where a contracting force is relatively small and there is flowability is maintained for a relatively long time, and a lens position error is gradually, finely, and continuously corrected in a hardening process until the gel state is changed to the solid state. As described above, a method for minimizing the optical alignment error is applied.
However, in such a method, since an epoxy hardening time is long, a product producing speed is reduced, and the price of products increases.
Therefore, it is required to shorten an epoxy hardening time, for securing productivity of products and price competitiveness.